Avian sarcoma virus replicates through a DNA intermediate that is inserted into the host cell chromosome. The mechanism of provirus integration, restrictions upon the insertion process and controls upon the expression of the integrated provirus will be studied. The analysis of the arrangement and location of the avian sarcoma provirus will be studied using restriction enzyme analysis and chromosome identification and fractionation. Individual cell clones containing different exogenous proviruses will be prepared for DNA analysis. Any cellular events reqiuired for insertion of the provirus will be studied and related to the observation that a cis-acting control requires cellular division for expression of any newly inserted provirus. The location and composition of several distinct endogenous RAV-O related DNA loci will be studied. The loci will be cloned and analyzed with respect to the viral sequence content (RAV-O related sequences) and the non-viral flanking sequences (non-RAV-O related).